In medical and other fields, a common way of detecting an antigen, antibody, or other analyte of interest is to utilise a specific or nonspecific binding partner or capture agent bound to, or immobilised, on a solid support. The sample potentially containing the analyte of interest is then brought into contact with the supported capture agent. After a period for reaction, a further, detecting reagent is added. This second reagent may be added before or after washing the solid support free of unbound sample. After a further reaction period to enable the detecting reagent to react with the analyte already reacted with, and bound to, the capture agent on the solid phase support, all unreacted material is removed from the site of reaction. In the final step, a process designed to reveal a label characteristic of the detecting reagent is used to reveal the presence of the detecting reagent bound to the analyte which in turn is bound to the capture agent on the solid phase support. The specificity of the result is conferred by the specificity of either or both of the capture and detecting reagents for the analyte.
The solid phase may be plastics, glass, metal, paper or porous membrane in any desired shape or size.
The capture agent may be antigen, antibody, lectin or other reagent having a reaction with the analyte of interest.
The detecting reagent may be antigen, antibody, lectin or other reagent having the capability of binding to the analyte, and labelled with an enzyme, radioisotope, fluorophore or heavy metal compound or other molecule or atom which may subsequently be detected with convenience to the user.
Such tests are frequently performed using a porous membrane or paper as the solid support. Sample, washing fluid and other reagents are added in sequence, each one passing through the membrane into a void space or absorbent material on the side of the membrane distal to the site of the reactions.
This method of performing the test is limited to samples which are either free of material of such a size as to block the pores of the membrane, or have been rendered free of such material by a procedure such as filtration or centrifugation, since blocked pores will inhibit the flow of washing fluids. The final step of detecting specifically-bound label will then be rendered very difficult because of the amount of unbound label remaining.
The present invention aims to provide an improvement to such methods.